(1) Field of the Invention
The present invention relates to a blade and to a method of fabricating the blade.
(2) Description of Related Art
During its rotary motion, a blade is subjected to a torsor of forces and is consequently subjected to a centrifugal force and also to multiple forces due to flapping, drag, and twisting movements, where twisting is caused in particular by the changes of pitch that seek to modify the angle of inclination of the blade relative to the plane of the hub supporting the blade. Such forces naturally generate bending and twisting moments.
The forces and the moments to which the blade is subjected due in particular to centrifugal force and to twisting then need to be transmitted by the blade to the hub.
The means for fastening the blade to the hub are then subjected to forces and moments that can be destructive, with the term “force” being used below to designate both forces and moments for reasons of simplification. Furthermore, it can be understood that it can be difficult to inspect a blade in order to see any potential damage. In addition, it is advantageous to optimize the fastener means in order to limit their weight and reduce the aerodynamic drag they generate in flight.
The technological background for blades, and in particular for propeller blades, includes numerous documents, and for example the following documents: RU 2 040 432 C1, RU 2 058 249 C1, RU 2 058 250 C1, RU 2 058 251 C1, GB 2 244 525, CA 1 321 735, GB 1 319 235, FR 2 312 673 A1, FR 2 639 021 A1, GB 2 443 482, GB 2 449 058 A, US 2008/075602 A1, U.S. Pat. No. 4,643,647 A, U.S. Pat. No. 4,664,600 A, U.S. Pat. No. 4,685,864 A, EP 1 484 475 A2, EP 1 669 547 A2, GB 2 440 345 A, US 2009/004008 A1, US 2009/035131 A1, EP 2 159 378 A2, FR 2 195 255 A, FR 2 605 586 A1, FR 2 682 992 A1, FR 2 683 764 A1, FR 2 684 719 A1, FR 2 685 249 A1, FR 2 685 732 A1, FR 2 732 406 A1, FR 2 906 320 A1, US 2006/257260 A1, FR 2 921 099 A1, US 2007/092379 A1, U.S. Pat. No. 5,022,824 A, U.S. Pat. No. 5,022,825 A, EP 0 362 886 A2, U.S. Pat. No. 5,017,092 A, GB 2 237 532 A, U.S. Pat. No. 5,127,802 A, U.S. Pat. No. 5,269,658 A, WO 93/08017 A1, WO 92/14646 A1, U.S. Pat. No. 5,163,817 A, WO 00/66429 A1, U.S. Pat. No. 6,213,719 B1, U.S. Pat. No. 4,302,155 A, U.S. Pat. No. 4,407,635 A, CA 401 168 A, U.S. Pat. No. 4,966,527 A, RU 2 001 828 C1, U.S. Pat. No. 5,240,377 A, CZ 1302 U1, FR 2 718 101 A1, RU 2 142 895 C1, SU 1 775 974 A1, RU 2 099 188 C1, US 2002/008177 A1, US 2003/156944 A1, US 2006/140772 A1, US 2008/187441 A1, US 2008/113179 A1, U.S. Pat. No. 7,503,750.
For example, document WO 93/08017 presents a blade provided with a spar subassembly having a metal retaining element and a cellular structure around which structural fibers are braided.
Document U.S. Pat. No. 4,302,155 presents a blade provided with a metal base pierced in its center to receive a pilot tube. The base includes a cylindrical portion and a cup-shaped portion defining a cavity, with foam extending from the cavity.
The foam and the base are then covered in fabric forming a rigid skin.
Furthermore, the blade includes collars for fastening to a hub that surrounds the rigid skin and the base.
The following documents are also known: DE 9114658, U.S. Pat. No. 3,754,840, and U.S. Pat. No. 5,222,297.
All of the forces to which the blade is subjected appear to pass via the base, it being difficult to look at that base because of the presence of the rigid skin.